Current generators (commonly referred to as current sources and current sinks) are important elements in the design of many electrical circuits. For example, current generators are used in differential amplifiers. Input voltages received at control electrodes of respective input transistors selectively divert the current provided by the current generator to change the output voltage of the amplifier. In many analog circuits, it is further necessary to provide a current whose magnitude is proportional to a reference voltage. For example, a voltage controlled oscillator often employs a voltage controlled current source. In commercial integrated circuits, it is desirable for the voltage-controlled current source to function under a variety of conditions, including variations in power supply voltage, temperature, and manufacturing process variations in which transistor thresholds vary. Some integrated circuits, once required to operate with a five-volt power supply voltage, must now function at a lower power supply voltage such as three volts. Thus, precision current generators are needed for low voltage operation.